A prosthetic socket for amputated limbs typically fits precisely and tightly to the residual limb to bear the weight of a patient previously placed on the now-missing limb, spreading the force from amputated bone ends and bone prominences and to soft portions of the residual limb. Fitting prosthetic sockets to residual limbs is carried out by an experienced prosthetist (as a prosthetic practitioner is called), and typically requires a high degree of training and experience. The typical process for making such sockets requires casting of the residual limb by wrapping with casting plaster (similar to making a fracture cast) to make a negative form, then filling the form with plaster to make a precise positive model of the residual limb.
The prosthetist must carefully evaluate the residual limb, alignment, stance and sensitivities, and determine the desired load bearing characteristics of the socket. Typically, to achieve a proper tight fit, the entire model must be reduced in circumference to some degree. In some areas, the model may be increased or material added to create pockets that reduce contact with sensitive areas of the residual limb. Using abrasive files, sand paper, and scraping tools, the prosthetist adjusts the diameter and shape of the model by hand, in an imprecise manner, to approximate the shape that is presumed to be appropriate for the intended outcome. Some prosthetists use computer scanning and manipulation to achieve this, but the process is still experience based and imprecise.
Once the model shaping process is complete, the socket is created by heating high temperature thermoplastics and forming them over the model using complicated and time-consuming techniques. Typically, over half of the materials required become scrap and must be disposed of. In many cases, the socket is made from fiberglass and toxic two-part resin. The resin must be cured, and forms a very rigid socket that can only be modified by grinding away material. These sockets are finished on the edges and surfaces using time-consuming and messy methods, and are then test fitted to the residual limb. Because the model shaping process is imprecise and based on estimation, often several time-consuming adjustments must be made to the socket for proper fitment, requiring several visits to the prosthetist and time consuming techniques to make adjustments.
This entire complicated process requires a large workshop with expensive machinery, ventilation, and extensive materials inventory, making it impractical to produce sockets in hospitals or off site. Many prosthetists perform only the initial casting and final fitting procedures because they do not have a sufficient workshop, and must send away to a socket making service further complicating the process and adding cost. Often, it is determined that the socket was improperly made and the entire process must be started again.
In the case of recent amputees, the residual limb is very sensitive, and over the period of months, can atrophy and shrink substantially, change shape, and develop callus. During this time, temporary “test” sockets are made using the above process, yet frequently with less durable materials because the sockets may only be worn for a short period until a subsequent one, started from scratch, is needed. This process may be repeated from three to five times depending on the amputation and amputee conditions, thereby significantly increasing the time, effort, waste, office visits, travel and efforts required of all involved.
This process is very stressful for the amputee. It is painful, time consuming, and often requires distant travel. It can take hours and days of waiting for adjustments to be made. The amputee typically must make several trips to the prosthetist and wait days or weeks for the socket to be completed. The process of making adjustment is limited, and therefore the entire process must be repeated if the prosthetist is unable to adjust the socket enough to achieve the desired results. Then, the amputee must get used to wearing the new socket which can involve weeks of pain, the final outcome being unknown until comfort is achieved.
Cost is another serious consideration. Insurance, which may covers prosthetics, can be extremely limited, and may not pay for another prosthetic for years, even if the current one is working poorly. For the prosthetist, insurance reimbursement is often a one-time fee based on the amputation and equipment approved. The number of times the prosthetic must be made and adjusted is not reimbursed for, and therefore the prosthetist loses profit every time the patient returns. The process is so difficult that amputees often put up with less than desirable fit, chronic pain, and use/walking challenges for months or even years before going through the process again.
In order to improve upon the challenges of making a socket in the conventional manner previously described, attempts have been made in the past to direct mold low temperature thermoplastic sockets onto residual limbs. These methods have not been widely accepted or used by prosthetists. Low temperature thermoplastic materials, such as polycaprolactone, have been used. Such materials are formable at between 120° F. and 180° F. (50° C. to 80° C.). They are typically heated in hot water and can be applied directly to the skin. These materials have inadequate strength and rigidity to hold up to the rigors of weight bearing and the abuse of walking. They also tend to become very difficult to work with because when heated they become clay like, extremely sticky and are very difficult to form tightly to the limb. Therefore, the sockets produced using these materials are inadequate and undesirable. While these sockets may occasionally be used as temporary sockets, they are typically not used as permanent sockets.
Other currently-used sockets have a hard supportive outer shell made in the typical fashion, and a softer, low temperature direct on-body heat-formed inner liner. While these sockets can perform adequately, they still require the same time-consuming steps needed to make the outer socket which is rigid, made of high temperature thermoplastics or fiberglass, and must be custom made using casting and a model as described above. Additional steps are required to mold the inner soft non-supportive liner using a heat forming direct-on-body process. If the outer hard socket is not properly formed and fitted, the inner soft liner may not adequately adjust to the residual limb.
Readily available low temperature thermoplastics used in the above-described methods are typically polycaprolactone or derivatives. This is because the plastics industry only recently developed thermoplastics that can be readily thermoformed at temperatures between 200° F. and 300° F. (between about 93° C. and 150° C.), and which have adequate physical properties. Temperatures above 300° F. are impractical because the residual limb would be burned by such hot materials applied to the body, even with an insulative liner. It should be noted that the physical properties for a prosthetic socket regarding durability, elongation, crack resistance and rigidity until recently were only achieved with materials thermoformed over 350° F. (about 176° C.) or with fiberglass and/or carbon fiber impregnated with resin.
The previously described methods of directly heat forming sockets to residual limbs have been largely unsuccessful and, as a result, are not prevalent in the market.